Many sporting activities employ an implement which has a tubular shaft structure, such as a hockey stick, lacrosse stick, golf club, and ski pole.
These and like tubular sport shafts were originally made from wood. More recently, the manufacture of tubular sport shafts has improved through the use of aluminum, graphite, and a variety of composite materials, including fiberglass and carbon fiber-reinforced plastics. However, these shaft designs and constructions have performance limitations and are subject to failure or breakage, even during ordinary play.
For example, a tubular sport shaft is typically performance-limited to a constant stiffness along the axial length of the shaft. To overcome this limitation, and to accommodate certain sporting applications or user preferences, manufacturers have provided shaft designs with variable axial stiffness by tapering the shaft or by applying more or less material to a given axial location. However, these techniques often form shafts that are unwieldy for the user and are difficult to manufacture.
Furthermore, the tubular shafts of the prior art can present significant danger to the user because of insufficient impact resistance and strength. Sporting records are constantly broken; and as the limits of physical achievement increase, the demands for integrity and longevity in the strength and resistance of the shaft also increases. Presently, tubular shafts fail during the ordinary course of play because they cannot withstand the variety of forces exerted on them. Once a tubular shaft fails, it is likely to project sharp or splintered edges that can cut or seriously injure the athletes.
Thus, further improvements are desired in the performance and construction of tubular, i.e. hollow, shafts. Accordingly, one object of the present invention is to provide a shaft suitable for sporting implements and which has improved impact resistance and bending strength, as compared to the prior shafts.
Another object of the invention is to provide an improved tubular shaft having selectively and controllable variable axial stiffness with constant cross-sectional area. A corollary object of the invention is to provide improvements to the manufacture of a tubular shaft having a selectively variable axial stiffness.
Still another object of the invention is to provide a shaft, suitable for example for a sporting implement, and which produces relatively few sharp edges and injurious splinters upon breakage.
Another object of the invention is to provide improvements in the structure and manufacture of composite members and materials which, for example, are suitable for use in the manufacture and construction of the above-described tubular sport shafts.
Composite materials and members are generally known, particularly in applications which require light weight and high strength. Such composite members typically have one or more plies, or layers, in combination with a polymer matrix. The geometry of the fiber components within the each ply or layer contributes to the strength and other physical properties of the composite member. U.S. Pat. No. 5,188,872 discloses one composite member having high bending strength. However, the structure and manufacture of this composite member has limitations when applied to the wide variety of tubular shafts used in sports such as hockey, golf, lacrosse and skiing.
Accordingly, the objects of the invention include providing composite members having improvements in impact resistance and bending strength.
Another object of the invention is to provide a composite member having selectively variable axial stiffness with constant cross-sectional area.
Yet another object of the invention is to provide improvements in the manufacture of composite members having variable axial stiffness.
These and other objects of the invention will become apparent in the description which follows.